The state of the art includes cartridge-type mixing valves which have a normally cylindrical cartridge body containing inside those functional elements to supply and restrict the hot and cold water to be mixed and delivered.
The cartridge body normally comprises a lower wall, or closure element, with two inlet holes, respectively associated with the supply pipes of the hot and cold water, and an outlet hole for the mixed water.
The different rates of flow of the water being fed are regulated by activating, by means of a lever, two plates, one stationary and the other movable, in such a way as to reduce or increase the apertures of the respective holes.
One of the most common disadvantages found in these mixing valves derives from the difference between the pressure, and therefore the flow, of delivery of the hot water and the cold water.
This difference in pressures derives from the different delivery points of the supply system from which the two types of water are supplied, and of the consequent different losses in load factor along the relative supply pipes.
In the more up-to-date mixing valves, the state of the art therefore includes, at the inlet to the mixing valve, an equalising device to equalise the two different pressures, thus making it possible to obtain at the outlet rates of flow of hot water and cold water substantially of the same entity.
One type of pressure regulator normally used in the state of the art includes a body, interposed between the supply pipes and the mixing valve and having the relative water inlet and water outlet holes, inside which there is a floating piston which moves towards one side or the other according to the differences in pressure with which the two types of water are supplied by the water supply system.
This movement of the floating piston causes an increase or a reduction in the inlet aperture of the feed channels of the water so that, when there is a condition of equal pressures and therefore the floating piston is stable, the two rates of flow delivered to the mixing valve are substantially equal.
In regulator devices known to the state of the art, it happens that at the end of its travel, both on one side and the other, the floating piston rests substantially with all its front surface on the wall of the body inside which it is contained.
This causes considerable imbalances in the thrust value acting on the piston, as this thrust is obtained as a product of the pressure and the surface.
A solution to this problem has been proposed in EP-A-599.998, which includes slots on the front walls of the piston.
This solution however does not resolve the problem in a satisfactory manner, as it causes difficulties in the working, imprecise regulation, possible imbalances and irregularities in the movement of the piston and other disdvantages.